diff --git a/application/core/Bills/BillData.php b/application/core/Bills/BillData.php
index 3129bcb5..b55a88a4 100644
--- a/application/core/Bills/BillData.php
+++ b/application/core/Bills/BillData.php
@@ -25,13 +25,13 @@ class BillData {
 	/**
 	 * Construct new Bill Data Model
 	 *
-	 * @param mixed         $function
+	 * @param callable      $function
 	 * @param Player|string $player
 	 * @param int           $amount
 	 * @param bool          $pay
 	 * @param string        $receiverLogin
 	 */
-	public function __construct($function, $player, $amount, $pay = false, $receiverLogin = null) {
+	public function __construct(callable $function, $player, $amount, $pay = false, $receiverLogin = null) {
 		$this->function      = $function;
 		$this->player        = $player;
 		$this->amount        = $amount;
diff --git a/application/core/Bills/BillManager.php b/application/core/Bills/BillManager.php
index 2d700c19..61187652 100644
--- a/application/core/Bills/BillManager.php
+++ b/application/core/Bills/BillManager.php
@@ -54,11 +54,7 @@ class BillManager implements CallbackListener {
 	 * @param string   $receiver
 	 * @return bool
 	 */
-	public function sendBill($function, Player $player, $amount, $message, $receiver = '') {
-		if (!is_callable($function)) {
-			trigger_error("Function is not callable!");
-			return false;
-		}
+	public function sendBill(callable $function, Player $player, $amount, $message, $receiver = '') {
 		$bill                   = $this->maniaControl->getClient()->sendBill($player->login, $amount, $message, $receiver);
 		$this->openBills[$bill] = new BillData($function, $player, $amount);
 		return true;